Bittner Eric R, Silva Carlos
Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, USA.
J Chem Phys. 2022 May 14;156(18):181101. doi: 10.1063/5.0090515.
Frenkel excitons are the primary photoexcitations in organic semiconductors and are ultimately responsible for the optical properties of such materials. They are also predicted to form bound exciton pairs, termed biexcitons, which are consequential intermediates in a wide range of photophysical processes. Generally, we think of bound states as arising from an attractive interaction. However, here, we report on our recent theoretical analysis, predicting the formation of stable biexciton states in a conjugated polymer material arising from both attractive and repulsive interactions. We show that in J-aggregate systems, 2J-biexcitons can arise from repulsive dipolar interactions with energies E > 2E, while in H-aggregates, 2H-biexciton states with energies E < 2E can arise corresponding to attractive dipole exciton/exciton interactions. These predictions are corroborated by using ultrafast double-quantum coherence spectroscopy on a [poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene)] material that exhibits both J- and H-like excitonic behavior.
弗伦克尔激子是有机半导体中的主要光激发，最终决定了这类材料的光学性质。据预测，它们还会形成束缚激子对，即双激子，这是多种光物理过程中的重要中间体。通常，我们认为束缚态源于吸引相互作用。然而，在此我们报告近期的理论分析，预测在一种共轭聚合物材料中，由于吸引和排斥相互作用会形成稳定的双激子态。我们表明，在J聚集体系统中，2J双激子可由能量E > 2E的排斥偶极相互作用产生，而在H聚集体中，能量E < 2E的2H双激子态可由吸引偶极激子/激子相互作用产生。通过对表现出J型和H型激子行为的[聚(2,5-双(3-十六烷基噻吩-2-基)噻吩并[3,2-b]噻吩)]材料进行超快双量子相干光谱实验，证实了这些预测。
